control cicuit

[Noori]

Control circuit.

Hi every one.

I want to install a new control circuit for air

conditioning split unit .The condencer has two

compressors with one refrigerant circuit while

the indoor unit has two gas circuits controled

by solenoid valve for part load.

Your cooperation to inform me the best way

to control the part load operation will be highly

appreciated.

best regard

[Brian_UK]

Firstly, what is wrong with the existing control system that you want to change it?

[nike123]

Control circuit.
Hi every one.
I want to install a new control circuit for air
conditioning split unit .The condencer has two
compressors with one refrigerant circuit while
the indoor unit has two gas circuits controled
by solenoid valve for part load.
Your cooperation to inform me the best way
to control the part load operation will be highly
appreciated.
best regard



What is size of system? I ask because I don't want to recommend something more expensive than system itself.

[Noori]

Firstly, what is wrong with the existing control system that you want to change it?
Dear Brian.
The condenser and the avaporatore are new and there is no controle board.
Thanks for your answer.

[Noori]

What is size of system? I ask because I don't want to recommend something more expensive than system itself.
Dear Nike123
The system size is 15tons withe two reciprocating hemetic COPLAND comprwssors 7.5tons each.
BEST REGARD.

[nike123]

Dear Nike123
The system size is 15tons withe two reciprocating hemetic COPLAND comprwssors 7.5tons each.
BEST REGARD.

Then your system could be efficiently controlled with one of programmable controllers from Carel pCo serie (http://www.carel.com/carelcom/web/eng/catalogo/gamma_dett.jsp?id_gamma=1&id_tipologiaProdotti=1&id_mercato=1) or Eliwell
Energy XT Pro (http://www.invensyscontrolseurope.com/InvensysControlsEurope/en/ProductsServices/Eliwell/ProgrammableControllers/) serie .

Check documentation to find appropriate one. I think that pCo1 (http://www.carel.com/carelcom/web/eng/catalogo/prodotto_dett.jsp?id_gamma=1&id_prodotto=3&id_mercato=1) could be cost-effective solution for your case.

Is this project same as in this discussion (http://www.refrigeration-engineer.com/forums/showthread.php?t=15350)?

What compressor model did you choose?

[malik55]

Are you building a system your self localy, I am asking becacuse normaly the standard BRANDED units such as Carrier, Trane, York, Airedale.... etc comes with its built in controls, and only you have to connect the matching electical cabels for indoor/outdoor units, otherwise if this is a mismatch unit, then you have to see what type of controls are availabe and what you wants to install, Availability of controls & cost is another factor, Needs some more details about your unit.

[Noori]

Then your system could be efficiently controlled with one of programmable controllers from Carel pCo serie (http://www.carel.com/carelcom/web/eng/catalogo/gamma_dett.jsp?id_gamma=1&id_tipologiaProdotti=1&id_mercato=1) or Eliwell
Energy XT Pro (http://www.invensyscontrolseurope.com/InvensysControlsEurope/en/ProductsServices/Eliwell/ProgrammableControllers/) serie .

Check documentation to find appropriate one. I think that pCo1 (http://www.carel.com/carelcom/web/eng/catalogo/prodotto_dett.jsp?id_gamma=1&id_prodotto=3&id_mercato=1) could be cost-effective solution for your case.

Is this project same as in this discussion (http://www.refrigeration-engineer.com/forums/showthread.php?t=15350)?

What compressor model did you choose?
Dear Nike123
The unit is YORK manufactured in EGYPT and imported without control panel , for the compressors are COPLAND reciprocating ( piston) Hermetic type.
THis project is the same in some points as the upove discussion.The condenser work in one gas circiut while the evaporatore has two gas citcuit controld by selonoid valve and I want to Know how I can control the unit running during the part load, can I closed the valve while the two compressors stillruning or I should stop the second one.
Best regard.

[Noori]

Are you building a system your self localy, I am asking becacuse normaly the standard BRANDED units such as Carrier, Trane, York, Airedale.... etc comes with its built in controls, and only you have to connect the matching electical cabels for indoor/outdoor units, otherwise if this is a mismatch unit, then you have to see what type of controls are availabe and what you wants to install, Availability of controls & cost is another factor, Needs some more details about your unit.
Dear Malik 55.
First thank u alot for your answer and I am happy to read your idea to solve this problem , u can read my answer to our friend Nike123 and u will fined mor information about the unit so I am waitting for your response withe my best regard.

[malik55]

How are both compressors piping is connected, discharge lines, liquid line and suction lines are single or double,
Do compressors has loading unloading system or you want to off half of the capacity as a part load?

[Noori]

How are both compressors piping is connected, discharge lines, liquid line and suction lines are single or double,
Do compressors has loading unloading system or you want to off half of the capacity as a part load?

Dear Malik55.
The compressors are working in parallel with one discharge line and one liquid line while the in door unit has on inlet header and one outlet header but with two gas circuit controlled by solenoid valve to close the refrigerant flow to one circuit .
There is no loading and un loading valves fixed with compressor so that the part load mean half of the full capacity

[malik55]

I think you can simply fix a 2 stage honeywell thermostat with 24 volt control transformer and 2 nos cooling relays if not available in the condensing unit. Use Y1 as 1st stage and Y2 as 2nd stage, If it is a pump down type then connect to solinoid coils only and let system starts up after pressure build up, but if there is no liquid line reciever then connect to the soliniod coil and compressor contactor and let both comes at same time, provide some on delay timer in Y1/Y2 cooling signal, if money is not a matter then you can fix a Seimens RX type controller. Hope your piping is designed well other wise system may face oil problems at partail load.

[Noori]

I think you can simply fix a 2 stage honeywell thermostat with 24 volt control transformer and 2 nos cooling relays if not available in the condensing unit. Use Y1 as 1st stage and Y2 as 2nd stage, If it is a pump down type then connect to solinoid coils only and let system starts up after pressure build up, but if there is no liquid line reciever then connect to the soliniod coil and compressor contactor and let both comes at same time, provide some on delay timer in Y1/Y2 cooling signal, if money is not a matter then you can fix a Seimens RX type controller. Hope your piping is designed well other wise system may face oil problems at partail load.

Dear Malik55
Yes I can use any two stage thermostat or any programmable controller but I am in need for your idea about the second compressor should I let it running or stop it during the unit half running.
Best regard.

[nike123]

If you let it running, then your evaporator and TEV valve will be small for that amount of pumped refrigerant and you are then going to face problems with low pressures.
Also, I think that you need some form of surge liquid receiver at common liquid line for periods when one compressor and one evaporator are in operation.

[malik55]

As I mentioned about the piping, if system piping is properly designed, then you will have no problem, try to run at partal load and observe, if there is compressor return oil problems, then run both curcuits.

[Noori]

If you let it running, then your evaporator and TEV valve will be small for that amount of pumped refrigerant and you are then going to face problems with low pressures.
Also, I think that you need some form of surge liquid receiver at common liquid line for periods when one compressor and one evaporator are in operation.

Dear Nike123.
Yes this is an expected for the evaporator pressure to becomes low as well as the condenser my be floated with liquid so that the condenser effective area will reduced and cause the space temperature to increase rapidly calling for the solenoid valve to open and run the second evaporator and so on.
Dear friend What u expected if I stop the second compressor during the half load.
Best regard .

[Noori]

As I mentioned about the piping, if system piping is properly designed, then you will have no problem, try to run at partal load and observe, if there is compressor return oil problems, then run both curcuits.

Dear malik55
Will u face such problem that the condenser has one refrigerant circuit while the evaporator has two refrigerant circuit controlled by solenoid valve.
will the unit runs probably whith one coperessor and one evaporator in this case.
Best regard.

[malik55]

If there is a liquid receiver in the system as nike mentioned and the condenser fans are controlled by some kind of speed contollers to maintain condenser pressure at partial loads, system may work with one unit running, but again I suspect normal oil return will be a problem,
Let both compressors sump equalized, provide an oil seperator and also a suction line accamulator.

[nike123]

If there is a liquid receiver in the system as nike mentioned and the condenser fans are controlled by some kind of speed contollers to maintain condenser pressure at partial loads, system may work with one unit running, but again I suspect normal oil return will be a problem,
Let both compressors sump equalized, provide an oil seperator and also a suction line accamulator.

The oil return control could be done with oil separators and oil equalization line, and, by intermittently switching both compressor ON for few minutes, to let the oil to return to the compressors. That is how it is done in VRF systems to.
That is why I recommended Carell PcO (or Energy XT Pro) as good programmable controller, because such functions (and condenser fan control) cold be easily programed.

Everything is already known from refrigeration racks, it only need some modifications to adapt to air conditioning purpose.

I am little amazed why there is no participation in this thread from more experienced RE members at field of equipment construction. :confused:
Or, there is no such a members here ???

[nike123]

Dear Nike123.
Yes this is an expected for the evaporator pressure to becomes low as well as the condenser my be floated with liquid so that the condenser effective area will reduced and cause the space temperature to increase rapidly calling for the solenoid valve to open and run the second evaporator and so on.
Dear friend What u expected if I stop the second compressor during the half load.
Best regard .



I think that you should stop second compressor during half load. Then you will experience over condensation without some mean of condensation control, and I suppose, that excessive refrigerant will stay in condenser or in surge liquid receiver (if fitted).

[Noori]

I think that you should stop second compressor during half load. Then you will experience over condensation without some mean of condensation control, and I suppose, that excessive refrigerant will stay in condenser or in surge liquid receiver (if fitted).

Dear Nike123
Dear MALIKE55.
Thank u a lot for your attention to my thread I will do the following.
1- Install a microcontroller for all the parameter discussed in the problem.
2- Using an equalized line for oil between the compressors.
3- Let the second compressor running for at lest two minutes in half load.
4- Using liquid receiver with volume approximately equal to the refrigerant volume in the second circuit of the evaporator.
5- Start the unit and check for the necessary refrigerant quantity depending on the suction line superheat and liquid line sub cooled.
Again I would like to send u my great thanks to your feed back.
Best regard.

[malik55]

Thanks for your appreciation,,
But Why you do not prefer to have a suction line accamulator, as due to variable load it will be possible that system will experience refrigerant flood back, it will not cost you much.

[Noori]

Thanks for your appreciation,,
But Why you do not prefer to have a suction line accamulator, as due to variable load it will be possible that system will experience refrigerant flood back, it will not cost you much.



Dear malik55.
Personally ,I prefer to use accumulator with oil separator because I found ( in more than on case ) that some of return oil was trapped in the accumulator if the system running with out using oil separator.
Actually, I face a large problem with the customer ,if I want to do a good job because good job is normally expensive.
Best regard.